Certain beverages are highly sensitive to temperature which can affect their appeal, both in taste and appearance. Beer, for example, is most flavorful and visually appealing when drunk in a narrow temperature range of from about 34.degree. to 38.degree. F. When beer is dispensed or poured directly from a refrigerated container, maintenance of the ideal drinking temperature presents no real problems.
Frequently, however, beer is stored in a large refrigerated cabinet or walk-in cooler and dispensed on tap at stations remote from the storage area. For example, in large meeting rooms, banquet halls, restaurants, or bars, the beer dispensing stations may be anywhere from 10 feet to 600 feet from the refrigerated storage area. Generally, the beer is delivered through suitable plastic or stainless tubing and the temperature control of the beer while traveling over such long distances requires relatively complex and expensive cooling systems. In effect, such temperature control systems comprise the combination of a basic refrigeration unit with a cooling medium for the delivery tubing.
The basic refrigeration unit comprises a closed system containing a low boiling refrigerant like freon, a compressor, a condenser coil, and an evaporator or chilling coil. Also included in the basic refrigeration unit is some type of electrical thermostatic control device for switching the compressor on and off as required to maintain the pre-set desired temperature.
The function of the cooling unit is to maintain the beer temperature in the delivery system connecting the beer storage and dispensing points. Typically, the delivery system, or line run, consists of beer tubing surrounded by or in contact with another tube adapted to carry a circulating coolant fluid which has been refrigerated to the desired temperature by the refrigeration unit. A variety of coolant fluids may be employed, but the one most commonly used in beer delivery systems of the type under consideration is a glycol-water mixture, and the cooling units using this liquid are commonly known as glycol units.
Conventional glycol units consist of an insulated container holding a relatively large volume, or bath, of the glycol-water mixture, on the order of 5 to 50 gallons. Coils of the refrigeration unit evaporator are positioned within the container and serve to chill the coolant liquid until it reaches the pre-set point of the temperature-sensitive thermostat whose sensing element is likewise immersed in the bath. The chilled coolant is then pumped from the container into the line run and back again. Despite its widespread usage, the described refrigeration unit-glycol unit cooling system was characterized by a number of disadvantageous features.
With control governed by thermostat, the coolant temperature could vary from the "on" set point of the thermostat to its "off" set point, a typical differential of from 3.degree. to 5.degree. F. Agitators were sometimes required to overcome the tendency for temperature stratification in the large volumes of coolant liquid. The sensitive thermostat and its associated electrical elements were subject to wear and breakdown necessitating replacement of those expensive parts.
Unnecessarily high operating expense was another undesirable attribute of the prior refrigeration-glycol systems. If a leak occurred in the coolant line, the cost of replacing the large volumes of glycol was high. When operating, the compressor was always running at full rated capacity, and the intermittent on-off cycles also caused electrical power surges for each start-up. Additionally, the warmed coolant was returned from the line run back into the bath which served as a temperature reservoir so that it was necessary to continually chill the large volume of coolant. The bath cooling also served as a limitation on the length of line run which could be employed because too great a length would cause excessive temperature rise of the coolant, thereby necessitating a much lower bath temperature in order to maintain the desired drinking temperature at the end dispensing station.
There thus exists a need for an improved refrigeration-glycol cooling system for remotely dispensed beverage applications.